Abstract
The so-called “sialo-chemical-biology” has become an attractive research area, as an increasing number of natural products containing a sialic acid moiety have been shown to play important roles in biological, pathological, and immunological processes. The intramolecular lactones of sialic acids are a subclass from this crucial family that could have central functions in the discrimination of physiological and pathological conditions. In this review, we report an in-depth analysis of the synthetic achievements in the preparation of the intramolecular lactones of sialic acids (1,4-, 1,7- and γ-lactones), in their free and/or protected form. In particular, recent advances in the synthesis of the 1,7-lactones have allowed the preparation of key sialic acid derivatives. These compounds could be used as authentic reference standards for their correct determination in biological samples, thus overcoming some of the limitations of the previous analytical procedures.
Highlights
Sialic acids (Sias) are a family of nine-carbon α-keto aldonic acids, including both the derivatives of the progenitor neuraminic acid (Neu, 5-amino-3,5-dideoxy-D-glycero-D-galacto-2-nonulosonic acid), as the N-acetylneuraminic acid (Neu5Ac) 1a and the N-glycolylneuraminic acid (Neu5Gc) 1b, and those of the later discovered 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid or 2-keto3-deoxy-D-glycero-D-galacto-nononic acid (KDN 1c), bearing a hydroxyl group in place of the amino group at the C5 position (Figure 1) [1,2,3,4,5,6,7,8].These carbohydrates possess several unique characteristics
Sias-containing natural compounds are often susceptible to structural biological modifications, generating a family of more than eighty distinct members [1,4,5]. Due to their peculiar structures, they present unique biochemical characteristics as compared to common monosaccharides [1,3,4,7]. They are biosynthesized by condensation of a neutral six-carbon unit sugar with pyruvate, and they are activated in the form of CMP- Sias (i.e., 2a–c) [1,4]
PPrrootteecctteedd 11,77‐-bbyycciicclliicc llaaccttoonneess 2200aa––cc aanndd 2211aa––cc aanndd ssyynntthheessiiss ooff tthhee ββ-‐22,88-‐uunnnnaattuurraall ssaacccchhaarriiddeess 2233aa––cc [[7755]]. These seminal studies reached several important goals, as they: (i) established synthetic routes for the synthesis of correct structuAres, which protected 1,4- and 1,7- lactones, yet1s,t7i-lbl iicnycalsicmlaifcrxettoeunreeso;f(Niie)ue5lAuccidated was not obvious; (iii) clarified the molecular mechanism leading to their their formation, which was alsoCbiznCtrl,icate;HsAhcowed their applicHa2t,ion in tNheHAbciological field
Summary
Sialic acids (Sias) are a family of nine-carbon α-keto aldonic acids, including both the derivatives of the progenitor neuraminic acid (Neu, 5-amino-3,5-dideoxy-D-glycero-D-galacto-2-nonulosonic acid), as the N-acetylneuraminic acid (Neu5Ac) 1a and the N-glycolylneuraminic acid (Neu5Gc) 1b, and those of the later discovered 3-deoxy-D-glycero-D-galacto-2-nonulosonic acid or 2-keto3-deoxy-D-glycero-D-galacto-nononic acid (KDN 1c), bearing a hydroxyl group in place of the amino group at the C5 position (Figure 1) [1,2,3,4,5,6,7,8]
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